Despite a spirited display, City lost 2-1 on the night and 4-1 on aggregate as the Catalans progressed to the quarterfinals at their expense.

Aguero, 25, started against Barca in what was only his third appearance since returning from a hamstring problem. But there is now a fear he may have aggravated that injury as he was withdrawn at the interval at Camp Nou, complaining of a tight hamstring.

Sergio Aguero could not help Manchester City turn their UCL tie around in Barcelona.

Aguero revealed after the match that he had suffered the injury in the third minute of the game when chasing down a ball with Lionel Messi.

“[I did it in] the move with Leo, right at the start of the game, after just three minutes,” Aguero told El Larguero. “I felt something there in my left leg. That stopped me from continuing. I was afraid about running into spaces. At half-time I got cold and said I would prefer to come out. I had some pain. Now I need to recover in the best way.”

City assistant Ruben Cousillas told reporters: "It's very early to say, so we cannot yet say how long he [Aguero] is going to be out. He felt some kind of pain in his muscle.

“We are doing some tests to assess it. It will be up to the medical staff who determine the extent of the injury, so we cannot speculate about this.”

Aguero said he had congratulated his friend Messi -- who scored the clincher early in the second half when capitalising on a Joleon Lescott error -- after the game.

“Of course -- we get on really well always,” he said. “We talked and I congratulated him, obviously. Before the game we always talk too. I always say [Messi] is the best player in the world, which makes me happy as he is Argentine.”

Another Argentina international who left the Camp Nou pitch early was City right-back Pablo Zabaleta, who was sent off by French referee Stephane Lannoy for disputing the decision not to award his side a late penalty for an apparent trip by Gerard Pique on Edin Dkezo.

“[Zabaleta] was pretty angry in the dressing-room about what happened,” Aguero said. “I asked him what happened and he said it was about the penalty. The truth is I never get involved with the referees. If they do not whistle they do not whistle. They can make mistakes too.”

City coach Manuel Pellegrini had perhaps shown too much respect for Barca in the first leg, Aguero hinted.

“We know that Barca have good feet,” he said. “Maybe for that we respected them a bit. But nothing, we try and play our own way. We could not do that. The most important game was there [first leg] and the penalty hurt us. We tried to do what we could here, knowing it was difficult.”

The former Atletico Madrid finished by saying he hoped his old side, who qualified for the quarterfinals by hammering AC Milan 4-1 on Tuesday, now went on to lift the trophy for the first time.

“In Spain my first team was Atletico Madrid,” Aguero said. “It is thanks to them that I am where I am today. I appreciate that a lot, what they did for me. I hope they can win it, I have great friends there. They have a great team, and if they keep playing like this they will have a big chance.”

Meanwhile, City now have just the Premier League to focus on -- having also been knocked out of the FA Cup by Wigan on Sunday -- with Pellegrini's side needing to claw back a nine-point gap between themselves and leaders Chelsea.